• 한국정밀공학회지
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• 제25권6호
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• pp.116-125
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• 2008

In general, fretting is a contact damage process due to micro-slip associated with small amplitude oscillatory movement between two surfaces in contact. Previous studies in fretting fatigue have observed a contact size effect related to contact width. The volume-averaging method of theoretically predicted contact stress fields was required to emulate experimental trends and to predict the observed contact size effects. This contact size effect is captured by the mean values of stresses and strains at the element integration points of FE model and two critical plane models (SWT, FS) in the present paper. It is shown that crack nucleation and fretting fatigue life can be predicted by the FE-based critical plane models.

• 대한화학회지
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• 제65권5호
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• pp.320-326
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• 2021

본 연구는 콘택트렌즈를 중합 시 사용하는 교차결합제의 구조가 콘택트렌즈의 물리적 특성 및 약물 용출에 미치는 영향을 조사하였다. 4종의 교차결합제를 0.3%와 3%를 각각 사용하여 콘택트렌즈를 제작하였으며 약물은 안약에 사용하는 ofloxacin을 사용하였다. 친수성 교차결합제를 사용한 콘택트렌즈는 함수율과 습윤성이 향상되었으며 친수성 작용기가 많을수록 효과가 크게 나타났다. 약물용출 농도는 친수성이 강한 교차결합제 사용 시 가장 높게 나타났으며 교차결합제의 농도가 높은 콘택트렌즈는 용출되는 약물 농도가 낮고 용출시간은 길어졌다. 콘택트렌즈의 교차결합제 구조는 콘택트렌즈의 성능 향상과 약물 방출조절에 영향을 주었다.

• Tribology and Lubricants
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• 제21권6호
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• pp.272-277
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• 2005

Continuously variable transmission (CVT) of toroidal type has a elliptical shape of contact zone under the elastohydrodynamic lubrication (EHL) condition, where the power is transmitted only by shearing the lubricant. Due to the small contact area of elliptical shape, the traction of the shear behaviors of lubricant over the contact zone is under extremely high contact pressure over 1.0GPa. During the power transmission by shearing the fluid, many kinds of mechanical movements occur such as squeezing, sliding, rolling and spin. Among the movements, the spin effect that is the most undesirable contact behavior in transmitting the power frequently makes significant abnormal wear damage. In this work, the analysis of elliptical contact of EHL with spin effect is performed, which will give very useful information to understand the traction behaviors in toroidal type of CVT system.

• 한국콘텐츠학회논문지
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• 제22권4호
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• pp.324-336
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• 2022

본 연구는 한국과 중국 소비자의 외식동기와 방문외식, 배달-테이크아웃 소비선택 간의 관계에서 코로나19로 인해 소비자들이 느끼는 대인접촉 불안감의 조절효과를 조사하고자 하였다. 한국소비자의 외식동기가 외식선택에 미치는 영향에서 대인접촉 불안감의 조절효과를 검증한 바, 대인접촉 불안감은 이성적동기가 방문외식에 미치는 정적 영향을 약하게 하는 조절효과가 있는 것으로 나타났다. 중국 소비자의 외식동기가 외식선택에 미치는 영향에서 대인접촉 불안감의 조절효과를 검증한 바, 이성적동기가 방문외식에 미치는 정적 영향은 약하게 하고, 감성적동기가 방문외식에 미치는 정적 영향은 강하게 하는 조절효과가 있는 것으로 나타났다. 또한 대인접촉 불안감은 이성적동기가 배달에 미치는 정적 영향은 강하게 하고, 감성적 동기가 배달에 미치는 정적 영향은 약하게 하는 조절효과가 있는 것으로 나타났으며, 감성적동기가 테이크아웃에 미치는 정적 영향은 강하게 하는 조절효과가 있는 것으로 나타났다.

• Tribology and Lubricants
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• 제26권1호
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• pp.56-60
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• 2010

Contact pressure occurs whenever two surfaces contact between cam and roller. Especially excessive pressure peaks occur at the ends of the contact region. Such as scuffing or pitting will be induced when these operating conditions continuously occur on the surface. Camber effect is given to reduce damage by changing the shape of roller. The objective of this paper is to calculate contact pressure distribution by using a contact analysis considering camber and tilting angle. These results predict that camber effect of all machine components have influence on contact pressure distribution.

• Human Ecology Research
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• 제62권2호
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• pp.217-231
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• 2024

The aims of this study were to identify (a) the social network contact frequency of the elderly with children, relatives, and friends; (b) the impact of contact frequency (face-to-face/non-face-to-face) on life satisfaction of the elderly; and (c) the moderating effect of digital capabilities of the elderly on the relationship between social contact frequency and life satisfaction. Data were obtained from the National Survey of Older Koreans 2020. The sample comprised 6,119 adults aged 65+ who were in single or couple households. The principal findings were as follows. First, couple households, higher levels of education, and better health status increased life satisfaction of the elderly. Second, the higher the frequency of face-to-face contact with children and the higher the frequency of non-face-to-face contact with friends, the more positive the effect on life satisfaction of the elderly. Third, the interaction effect of the digital capabilities of the elderly differed according to children, relatives and friends. There was a significant and positive moderating effect on the relationship between life satisfaction and the frequency of face-to-face/non-face-to-face contact with children and the frequency of face-to-face contact with relatives. Conversely, there was a significant negative effect on the relationship between life satisfaction and the frequency of face-to-face/non-face-to-face contact with friends. By examining the impact of non-face-to-face contact on life satisfaction of the elderly in the era of digital transformation, the findings have significance in that they provide basic data to support policies and education programs aimed at improving the digital capabilities of the elderly.

• 대한기계학회논문집
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• 제18권11호
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• pp.2967-2972
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• 1994

The multiple character of the contact interaction and the collective behavior of elementary microcontacts play a significant role in all the processes occurring in the surface layers, including the failure due to friction and wear. The array of metal spheres compressed between flat plates has been used for simulation of the contact behavior of multiple contact of solids under normal loading. An experimental design has been made providing regular array of the spheres at the same size with different spatial order. Measurement of electrial contact resistance has been made using the equipment providing the adequate accuracy in the range of micro Ohms. The data on electrical contact resistance have been compared with theoretical predictions using the multiple contact model of constriction resistance. The effect of single spots number and array on conductivity of contact has been evaluated.

• Tribology and Lubricants
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• 제18권4호
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• pp.249-254
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• 2002

Adhesive contact characteristics of torus-shaped bumps were analyzed using the finite element technique considering the adhesive force. Analyses focused on the effect of rim and bump radii on the adhesive contact behavior such as the jump-to-contact behavior, adhesion hysteresis, pull-off forces, contact region and pressure, and surface and subsurface stresses. Analysis results in the absence of adhesive force were also included to examine the effect of adhesive force. The applicability of torus-shaped bumps to the MEMS structure for reduction of friction is discussed.

• Geomechanics and Engineering
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• 제28권2호
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• pp.107-116
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• 2022

The steady state of unsaturated soil takes a long time to achieve. The soil seepage behaviours and hydraulic properties depend highly on the wetting/drying rate. It is observed that the soil-water characteristic curve (SWCC) is dependent on the wetting/drying rate, which is known as the dynamic effect. The dynamic effect apparently influences the scanning curves and will substantially affect the seepage behavior. However, the previous models commonly ignore the dynamic effect and cannot quantitatively describe the hysteresis scanning loops under dynamic conditions. In this study, a dynamic hysteresis model for SWCC is proposed considering the dynamic change of contact angle and the moving of the contact line. The drying contact angle under dynamic condition is smaller than that under static condition, while the wetting contact angle under dynamic condition is larger than that under static condition. The dynamic contact angle is expressed as a function of the saturation rate according to the Laplace equation. The model is given by a differential equation, in which the slope of the scanning curve is related to the slope of the boundary curve by means of contact angle. Empirical models can simulate the boundary curves. Given the two boundary curves, the scanning curve can be well predicted. In this model, only two parameters are introduced to describe the dynamic effect. They can be easily obtained from the experiment, which facilitates the calibration of the model. The proposed model is verified by the experimental data recorded in the literature and is proved to be more convenient and effective.

• 소성∙가공
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• 제20권2호
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• pp.99-103
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• 2011

Many parameters influence the frictional behavior of steel sheet during stamping. The contact pressure between a die and a sheet during stamping is one of them. Thus, this parameter is investigated for high strength steel (HSS) sheets, which are widely used for auto body panels due to their potential for weight reduction. Since HSS extend the limits of contact pressure for mild steel, the effect of this parameter on friction cannot be ignored. To investigate the influence of contact pressure on the frictional behavior of steel sheets, a flat type of friction test was conducted on three different steel sheets under various contact pressures. For bare steel sheets, the curve representing the relationship between contact pressure and friction coefficient exhibits a U shape. Coated steel sheets show a similar tendency except at low contact pressure. For these materials, when the contact pressure is very low, the friction coefficient slightly increases with pressure before it starts to decrease. The test results show that the effect of contact pressure on frictional behavior of steel sheet is not negligible even for contact pressures that are lower than the strength of HSS sheet.